1. Field of the Invention
The present invention relates to mobile antennas mounted on the body of a vehicle and configured to receive radio waves within, for example, television broadcast bands.
2. Description of the Related Art
Mobile antennas for receiving radio waves within television broadcast bands include rod antennas, film antennas, and the like. In recent years, film antennas have been becoming mainstream because they have hard deformation characteristic and low impact on the appearance of the vehicle body without causing wind noises.
These types of mobile antennas require to have a wideband characteristic capable of receiving a plurality of channels within the VHF band and the UHF band, and a nondirectional characteristic for receiving radio waves in all directions independently of any direction of travel.
An example of these types of mobile antennas is disclosed in Japanese Unexamined Patent Publication No. 2004-72419.
Assuming that a mobile antenna disclosed in the Patent Publication is mounted at the middle portion of the top edge of a front windshield of a vehicle, if radio waves are transmitted from the front side of the vehicle, the mobile antenna can efficiently receive the radio waves transmitted from the front side of the vehicle.
In contrast, in this assumption, if radio waves are transmitted from the rear side of the vehicle, because the radio waves are shielded by the vehicle body, the mobile antenna may not efficiently receive the radio waves transmitted from the rear side of the vehicle. This may cause the receiving efficiency of the mobile antenna with respect to the radio waves transmitted from the rear side of the vehicle to decrease.
In order to solve the problem, it is to be considered that the mobile antennas disclosed in FIG. 13 of the Patent Publication are mounted to be spaced along the top edge of a front windshield of a vehicle to constitute a diversity system. Specifically, the diversity system is configured such that output signals from the mobile antennas based on the received radio waves thereby are combined to give a single signal. It may be difficult for the diversity system, however, to improve the receiving efficiency of each of the mobile antennas with respect to radio waves transmitted from the rear side of a vehicle.